Pro - Someone else does the work for you.Con - You have to pay someone else to do the work for you.

To be clear, you are not paying off the 80K mortgage.

I pay for prop stream and love the amount of detail you can add into a search. 

Also never pay any upfront fees and go with a trusted lender who closes through a title company. 

Please see the rough numbers below :Tear down house price 350k,Construction cost 165 sqft * 2 build=627k too much for the land unless your exit is 3 million. don't reinvent the wheel. no single family home builder is paying 300k for land. that's miami florida prices where I live. we buy land 50k and under in Columbus Ohio. keep land at less than 10% of after built value.

The paid off student rental plus the 2nd student rental helps pays off the mortage for 2nd student rentals and living expenses for me and my wife. the duplex was  cash flowing approx  $300 month with the old tenants We manage everything ourselves with some help from our family. 

If this is simply you not wanting to accept partial payments and the rent is current, stop accepting it - and send a Lease Violation/Notice of Quit for Non-Payment of Rent - and force the full rent to be paid per the lease or start eviction.  

Relatively small amounts of interest income ($1600+ per year) is the highest taxed form of income I have found if you have kids at home.After earning a few grand in interest, It takes away my child tax credits and gives me an effective tax rate of 70%.   

I currently live in a 1000 sqft home that we pay a mortgage on.

You can't actually pay it off directly because they've been securitized, and the people who invested in those securities did so because of the specific certainty of the payment schedule.What you do in a defeasance is use the proceeds of the sale or the funds from your new lender to purchase treasury bonds that are packaged to make the exact payment amounts and timings on the remaining term of the loan, and then assign those bonds to your old lender.